Core System Architecture Part 101 — Anonymous Network Capacity Management, Load Shedding, Admission Control, Autoscaling, Resource Fairness & Privacy-Preserving Availability Architecture
SIAR — Secure, Local-First, Multi-Transport Communication Platform
Series: Core System Architecture
Part: 101
Status: Architecture specification
Primary language: Rust
Builds on: Core System Architecture Parts 8, 12–13, 17, 49–53, 63, 69–70, 74–80, 92, 95–100
Primary purpose: define SIAR's capacity-management architecture for service/resource budgets, admission control, overload detection, backpressure, queue isolation, autoscaling, regional capacity, load shedding, brownout modes, tenant/anonymous-user fairness, protected critical traffic, cost-aware scaling, privacy-safe telemetry, and resilient availability without relying on stable user identity or behavioral profiling.
1. Purpose
Capacity management decides what happens when demand approaches or exceeds available resources.
Without explicit architecture, overloaded systems often fail by:
unbounded queues
memory exhaustion
cascading retries
latency collapse
priority inversion
tenant starvation
privacy downgrade
The governing principle is:
SIAR should preserve the most important security, control, and communication capabilities under load by bounding work, isolating resources, shedding low-priority demand first, and scaling from privacy-safe operational signals rather than user profiling.
2. Architectural Position
Incoming Work
│
▼
Admission Control
│
▼
Priority / Fairness Classification
│
▼
Bounded Queue / Resource Budget
│
├── Execute
├── Backpressure
├── Defer
└── Shed
│
▼
Capacity / Autoscaling Feedback
3. Core Separation
Keep distinct:
capacity
admission
priority
fairness
quota
backpressure
load shedding
autoscaling
billing
4. Non-Goals
Part 101 does not create:
per-user behavioral priority
pay-to-bypass security controls
unbounded burst handling
autoscaling based on private content
availability via privacy downgrade
5. Resource Dimensions
#![allow(unused)] fn main() { pub enum ResourceDimension { Cpu, Memory, DiskIo, NetworkIngress, NetworkEgress, Connections, QueueDepth, Storage, FileDescriptors, CryptoOperations, } }
6. Hard Rule
Capacity decisions must identify the actual constrained resource.
7. Service Capacity Model
#![allow(unused)] fn main() { pub struct ServiceCapacityModel { pub service: ServiceId, pub budgets: Vec<ResourceBudget>, pub overload_policy: OverloadPolicy, } }
8. Resource Budget
#![allow(unused)] fn main() { pub struct ResourceBudget { pub dimension: ResourceDimension, pub soft_limit: u64, pub hard_limit: u64, } }
9. Soft Limit
Triggers pressure response.
10. Hard Limit
Must not be exceeded.
11. Hard Rule
Hard resource limits are enforced, not advisory.
12. Capacity State
#![allow(unused)] fn main() { pub enum CapacityState { Normal, Elevated, Saturated, Critical, Recovering, } }
13. Normal
Healthy headroom.
14. Elevated
Pressure building.
15. Saturated
Near resource ceiling.
16. Critical
Risk of service collapse.
17. Recovering
Pressure reduced but system not yet stable.
18. No Critical→Normal Jump
Hard rule.
19. Hysteresis
Required to avoid oscillation.
20. Capacity Thresholds
#![allow(unused)] fn main() { pub struct CapacityThresholds { pub elevated: FixedPoint, pub saturated: FixedPoint, pub critical: FixedPoint, pub recovery: FixedPoint, } }
21. Recovery threshold lower than entry threshold.
22. Hard rule.
23. Work Classes
#![allow(unused)] fn main() { pub enum WorkClass { CriticalSecurity, EmergencyRealtime, ControlPlane, DirectMessaging, Interactive, Background, Bulk, Optional, } }
24. CriticalSecurity
Examples:
credential revocation
key rotation
security update
incident containment
25. EmergencyRealtime
Emergency call/message.
26. ControlPlane
Identity, config, service discovery, quorum.
27. DirectMessaging
Normal user messaging.
28. Interactive
Search/settings/feed interactions.
29. Background
Sync/maintenance.
30. Bulk
Attachments/backups.
31. Optional
Analytics/prefetch/nonessential work.
32. Hard Rule
Work class is semantic, not user-status based.
33. Priority Order
Recommended:
CriticalSecurity
> EmergencyRealtime
> ControlPlane
> DirectMessaging
> Interactive
> Background
> Bulk
> Optional
34. Privacy Floor
Priority never allows privacy downgrade.
35. Hard rule.
36. Protected Capacity
Reserve headroom for high-priority work.
37. Protected Capacity Policy
#![allow(unused)] fn main() { pub struct ProtectedCapacity { pub class: WorkClass, pub minimum_share: FixedPoint, } }
38. Example
Reserve CPU/queue slots for:
security revocation
identity
emergency
39. Hard Rule
Low-priority floods cannot consume all protected capacity.
40. Resource Pools
Separate where practical.
41. Example:
realtime pool
control pool
bulk pool
background pool
42. Why
Prevents head-of-line blocking.
43. Hard rule.
44. Queue Architecture
Every queue bounded.
45. Queue Budget
#![allow(unused)] fn main() { pub struct QueueBudget { pub max_items: usize, pub max_bytes: usize, pub max_age: Duration, } }
46. No Unbounded Channel
Hard rule.
47. Tokio Channels
Bounded.
48. Blocking Work
Dedicated bounded blocking pools.
49. Hard rule.
50. Queue State
#![allow(unused)] fn main() { pub enum QueueState { Healthy, Pressured, Full, Draining, } }
51. Backpressure
Preferred before failure.
52. Backpressure Mechanisms
await capacity
reduce producer rate
pause optional fetch
defer bulk transfer
return retry-after
53. Hard Rule
Backpressure propagates toward producer rather than accumulating hidden memory.
54. Admission Control
Decides whether new work enters.
55. Admission Decision
#![allow(unused)] fn main() { pub enum AdmissionDecision { Admit, AdmitDegraded, Queue, RetryLater, Reject, } }
56. Admit
Normal execution.
57. AdmitDegraded
Reduced optional features.
58. Queue
Durable bounded defer.
59. RetryLater
Caller should retry with policy.
60. Reject
Cannot accept safely.
61. Hard Rule
Admission decision is explicit and observable.
62. Admission Context
#![allow(unused)] fn main() { pub struct AdmissionContext { pub class: WorkClass, pub resource_cost: EstimatedResourceCost, pub scope: AdmissionScope, } }
63. Admission Scope
#![allow(unused)] fn main() { pub enum AdmissionScope { Anonymous, Relationship(RelationshipId), Tenant(TenantId), Service(ServiceId), FederationPeer(FederationDomainId), } }
64. No Global User Identity Required
Hard rule.
65. Estimated Resource Cost
#![allow(unused)] fn main() { pub struct EstimatedResourceCost { pub cpu_units: u32, pub memory_bytes: u64, pub io_bytes: u64, pub network_bytes: u64, } }
66. Estimate Can Be Coarse
67. No need to inspect private payload semantics.
68. Hard rule.
69. Admission Controller
#![allow(unused)] fn main() { pub trait AdmissionController { fn decide( &self, ctx: &AdmissionContext, state: &CapacitySnapshot, ) -> AdmissionDecision; } }
70. Deterministic/typed.
71. No remote ML black box baseline.
72. Hard rule.
73. Anonymous Fairness
Anonymous users cannot be allocated by stable identity.
74. Use scoped short-lived mechanisms.
75. Examples:
capability token
anonymous quota token
connection bucket
proof-of-work/cost token if needed
76. No permanent tracking identifier.
77. Hard rule.
78. Fairness Model
#![allow(unused)] fn main() { pub enum FairnessScope { AnonymousCapability, Tenant, FederationPeer, ServiceClass, } }
79. No GlobalUser.
Hard rule.
80. Fair Share
#![allow(unused)] fn main() { pub struct FairShare { pub scope: FairnessScope, pub weight: u32, pub burst: u32, } }
81. Weighted Fair Queuing
Good fit.
82. Deficit Round Robin
Also suitable.
83. No strict FIFO across all traffic.
84. Hard rule.
85. Tenant Fairness
Each tenant gets bounded share.
86. Prevent noisy neighbor.
87. Enterprise tiers may have contracted capacity.
88. But
security/control capacity remains protected.
89. Hard rule.
90. Anonymous Network Fairness
Capacity assignment should not require deanonymization.
91. Good primitives:
scoped bearer quota
blind/anonymous token
per-connection fairness
92. No stable account identity.
93. Hard rule.
94. Federation Fairness
Per peer/domain quotas.
95. No remote user identity.
96. Hard rule.
97. Abuse vs Capacity
Separate concepts.
98. Capacity handles resource pressure.
99. Abuse controls malicious behavior.
100. Do not infer maliciousness merely from heavy legitimate usage.
101. Hard rule.
102. Rate Limiting Integration
Part 44.
103. Rate limit by:
capability
tenant
service endpoint
federation peer
104. Not global user unless authenticated managed scope explicitly needs.
105. Hard rule.
106. Token Bucket
#![allow(unused)] fn main() { pub struct TokenBucketPolicy { pub refill_per_second: u64, pub burst: u64, } }
107. Separate bucket per work class.
108. Critical traffic cannot share low-priority bucket.
109. Hard rule.
110. Concurrency Limits
Essential.
111. Example:
max concurrent uploads
max concurrent DB queries
max active crypto jobs
max relay streams
112. Concurrency Semaphore
Bounded.
113. No queue-behind-unbounded semaphore.
114. Hard rule.
115. Load Shedding
Drop/defer low-priority work when overloaded.
116. Shedding Order
Recommended:
Optional
→ Bulk
→ Background
→ Interactive extras
117. Do Not Shed
critical revocation
security policy
emergency communication
control-plane quorum
unless physically impossible.
118. Hard rule.
119. Load Shedding Decision
#![allow(unused)] fn main() { pub enum SheddingAction { DisableOptionalFeature, DropCacheWarmup, PauseBulkTransfer, DeferBackgroundSync, ReduceResultSize, RejectNewWork, } }
120. No Privacy Shedding
Never:
disable encryption
disable anonymity
skip authorization
121. Hard rule.
122. Brownout Mode
Reduce nonessential features before outage.
123. Brownout Features
Examples:
disable recommendations
disable previews
reduce feed page size
pause analytics
delay attachment transfers
124. Keep core messaging/security.
125. Hard rule.
126. Brownout State
#![allow(unused)] fn main() { pub enum BrownoutLevel { None, Level1, Level2, Level3, } }
127. Level1
Optional features off.
128. Level2
Bulk/background constrained.
129. Level3
Core services only.
130. Explicit UI/ops state.
131. No hidden behavior.
132. Hard rule.
133. Retry Architecture
Retries can amplify overload.
134. Use:
exponential backoff
jitter
retry budget
server retry-after
135. Retry Budget
#![allow(unused)] fn main() { pub struct RetryBudget { pub max_attempts: u8, pub max_elapsed: Duration, } }
136. No infinite retries.
137. Hard rule.
138. Retry Storm Protection
Server can return coarse backoff class.
139. Clients honor.
140. No synchronized fixed retry interval.
141. Hard rule.
142. Circuit Breakers
Useful for failing dependencies.
143. Circuit State
#![allow(unused)] fn main() { pub enum CircuitState { Closed, Open, HalfOpen, } }
144. Scope per downstream dependency.
145. No global circuit for unrelated services.
146. Hard rule.
147. Bulkhead Isolation
Separate resources across dependency/service classes.
148. Failure in media service should not exhaust identity service.
149. Hard rule.
150. Autoscaling
Scale based on resource/service pressure.
151. Allowed Signals
CPU
memory
queue depth
request latency
active connections
throughput
152. Forbidden Baseline Signals
user identity
message content
search interests
feed behavior
contact graph
153. Hard rule.
154. Autoscaling Metric
#![allow(unused)] fn main() { pub struct ScalingMetric { pub dimension: ResourceDimension, pub observed: u64, pub target: u64, } }
155. Autoscaling Decision
#![allow(unused)] fn main() { pub enum ScalingDecision { NoChange, ScaleOut(u16), ScaleIn(u16), } }
156. Scale-Out
Add capacity.
157. Scale-In
Careful/drained.
158. No instant scale-in during recovery.
159. Hard rule.
160. Autoscaling Controller
#![allow(unused)] fn main() { pub trait AutoscalingController { fn decide( &self, state: &CapacitySnapshot, policy: &AutoscalingPolicy, ) -> ScalingDecision; } }
161. Autoscaling Policy
#![allow(unused)] fn main() { pub struct AutoscalingPolicy { pub min_instances: u16, pub max_instances: u16, pub cooldown: Duration, pub scale_out_threshold: FixedPoint, pub scale_in_threshold: FixedPoint, } }
162. Hysteresis + Cooldown
Required.
163. Hard rule.
164. Privacy-Safe Autoscaling
Metrics aggregate by service/region.
165. No per-user series.
166. Hard rule.
167. Anonymous Traffic Scaling
Scale by total queue/throughput.
168. No need to identify users.
169. Hard rule.
170. Regional Autoscaling
Per region.
171. Respect residency.
172. No moving sensitive load to forbidden region.
173. Hard rule.
174. Capacity Headroom
Reserve for spikes.
175. Headroom Policy
#![allow(unused)] fn main() { pub struct CapacityHeadroom { pub minimum_percent: FixedPoint, pub critical_reserve_percent: FixedPoint, } }
176. Critical reserve not consumed by optional work.
177. Hard rule.
178. Capacity Forecasting
Can use aggregate time series.
179. Examples:
daily peak
release event
school-hour usage
regional trend
180. No user-level prediction.
181. Hard rule.
182. Forecasting Inputs
Operational aggregates only.
183. Long-term planning.
184. No real-time decision based solely on forecast.
185. Hard rule.
186. Capacity Planning
Part 63 integration.
187. Need:
steady state
peak
failure mode
growth
recovery reserve
188. Test under fault.
189. Hard rule.
190. Cost-Aware Scaling
Possible.
191. Cost must not override security/privacy minimum.
192. Hard rule.
193. Cost Policy
#![allow(unused)] fn main() { pub struct CapacityCostPolicy { pub max_hourly_cost: Money, pub emergency_override: bool, } }
194. Emergency override allowed for critical service continuity.
195. Audited at policy level.
196. Hard rule.
197. Cost Shedding
If budget constrained:
shed optional/bulk/background
198. Not encryption/anonymity/control plane.
199. Hard rule.
200. Storage Capacity
Need quotas + GC.
201. Storage Classes
#![allow(unused)] fn main() { pub enum StorageClass { CriticalMetadata, Messages, Attachments, Cache, Logs, Backups, Analytics, } }
202. Deletion Order Under Pressure
Prefer:
expired cache
expired logs
expired analytics
rebuildable state
before authoritative data.
203. Hard rule.
204. Storage Emergency
If disk nearly full:
stop bulk ingest
pause attachments
protect DB WAL/headroom
205. Do not corrupt authoritative DB.
206. Hard rule.
207. Memory Pressure
Actions:
trim caches
reduce concurrency
shed optional work
208. No OOM-as-policy.
209. Hard rule.
210. CPU Pressure
Reduce:
background encoding
index rebuild
bulk crypto
analytics
211. Preserve critical crypto/auth.
212. Hard rule.
213. Network Egress Pressure
Prioritize:
control
direct messages
emergency
over:
attachments
backups
analytics
214. Hard rule.
215. Connection Pressure
Limit:
idle connections
bulk transfer concurrency
216. Reuse connections.
217. No mass disconnect of control/security channels.
218. Hard rule.
219. Database Capacity
Protect connection pool.
220. Query Classes
critical writes
interactive reads
background jobs
analytics
221. Separate pool/priority where possible.
222. Hard rule.
223. DB Admission
Reject/defer expensive low-priority query under pressure.
224. Never allow analytics to exhaust production connection pool.
225. Hard rule.
226. Queue Durability
Only some queues durable.
227. Durable:
message outbox
critical jobs
billing/accounting tasks
228. Ephemeral:
cache refresh
prefetch
analytics flush
229. Hard rule.
230. Durable Queue Pressure
Need spill/partition/retention.
231. Cannot simply drop authoritative work.
232. May stop admission.
233. Hard rule.
234. Anonymous Mailbox Capacity
Per mailbox capability quota.
235. No global identity.
236. Under abuse:
quota
proof
token
expiration
237. No deanonymization.
238. Hard rule.
239. Mixnet Capacity
Special.
240. Real/cover traffic interaction.
241. Under pressure:
shed optional cover first within privacy floor
reduce bulk anonymous transfers
preserve minimum cover schedule
242. Hard Rule
Never reduce cover below configured privacy floor just to increase throughput.
243. Mix Node Admission
Bound packets/queues.
244. No unbounded packet buffering.
245. Hard rule.
246. Cover Traffic Budget
#![allow(unused)] fn main() { pub struct CoverTrafficBudget { pub minimum_rate: u64, pub target_rate: u64, pub maximum_rate: u64, } }
247. Minimum is privacy floor.
248. Hard rule.
249. Anonymous Attachment Transfer Capacity
Defer/throttle bulk.
250. No direct path fallback.
251. Hard rule.
252. Realtime Calls
Need bounded admission.
253. Call Capacity
#![allow(unused)] fn main() { pub struct RealtimeCapacity { pub max_sessions: u32, pub reserved_emergency_sessions: u32, } }
254. When full:
reject new normal call
preserve emergency reserve
255. Hard rule.
256. Media Degradation
Can lower bitrate/quality.
257. But no unencrypted fallback.
258. Hard rule.
259. Search Capacity
Reduce result count.
260. Defer federated fanout.
261. Local search unaffected.
262. No private query centralization.
263. Hard rule.
264. Notification Capacity
Aggregate low-priority notifications.
265. Preserve security alerts.
266. Hard rule.
267. Feed Capacity
Fallback to chronological/local cache.
268. Disable recommendation extras first.
269. Hard rule.
270. Analytics Capacity
Pause entirely if needed.
271. Analytics loss acceptable.
272. Hard rule.
273. Backup Capacity
Throttle background backup.
274. Do not starve minimum RPO forever.
275. Hard rule.
276. Update Capacity
Security update distribution high priority.
277. Routine update lower.
278. Hard rule.
279. DR Capacity Reserve
Keep reserve for failover/recovery.
280. Normal load should not consume all standby capacity.
281. Hard rule.
282. Regional Failure Capacity
Remaining regions must absorb failover.
283. Capacity plan includes N-1 failure.
284. Critical systems maybe N-2.
285. Hard rule.
286. Failover Admission
During regional loss:
preserve existing sessions
limit bulk/new optional work
287. Avoid secondary collapse.
288. Hard rule.
289. Autoscaling Failure
Need static safe floor.
290. If autoscaler unavailable:
fixed minimum fleet
manual control
load shedding
291. No uncontrolled scale-to-zero.
292. Hard rule.
293. Capacity Control Plane
Must not depend on overloaded data plane.
294. Separate resources.
295. Hard rule.
296. Scheduler Architecture
Resource-aware scheduling.
297. Scheduler Input
#![allow(unused)] fn main() { pub struct SchedulingRequest { pub class: WorkClass, pub cost: EstimatedResourceCost, pub scope: FairnessScope, pub deadline: Option<Duration>, } }
298. Scheduler Decision
#![allow(unused)] fn main() { pub enum SchedulingDecision { RunNow, Queue, Defer, Reject, } }
299. No behavioral priority.
300. Hard rule.
301. Deadline Scheduling
Useful for realtime/control.
302. But deadline cannot bypass hard resource limits.
303. Hard rule.
304. Fair Scheduler
Recommended:
weighted fair queueing
+
priority ceilings
+
protected reserves
305. Prevent tenant domination.
306. Prevent priority starvation.
307. Hard rule.
308. Priority Inversion
Need prevention.
309. Example:
Bulk lock holds resource needed by security task.
310. Use:
small critical sections
separate pools
priority inheritance where appropriate
311. Hard rule.
312. Starvation Prevention
Low-priority work needs bounded progress when healthy.
313. During sustained crisis
may remain deferred.
314. Explicit.
315. Hard rule.
316. Capacity Leases
Possible for expensive jobs.
317. Lease expires.
318. Prevent orphaned resource reservation.
319. Hard rule.
320. Admission Tokens
Could represent short-lived resource entitlement.
321. Anonymous-capable.
322. No long-lived identity.
323. Hard rule.
324. Anonymous Resource Token
#![allow(unused)] fn main() { pub struct AnonymousResourceToken { pub class: WorkClass, pub units: u32, pub expires_at: Timestamp, } }
325. Signed/blind if privacy architecture supports.
326. No custom crypto baseline.
327. Hard rule.
328. Tenant Quota
Separate from billing.
329. Quota says resource entitlement.
330. Billing says payment accounting.
331. Hard rule.
332. Quota Policy
#![allow(unused)] fn main() { pub struct TenantQuota { pub tenant: TenantId, pub resource: ResourceDimension, pub sustained: u64, pub burst: u64, } }
333. Tenant A quota cannot affect B except shared physical pressure.
334. Hard rule.
335. Shared Pressure Fairness
When shared resource saturated:
minimum fair share
weighted excess
336. No zeroing small tenants.
337. Hard rule.
338. Federation Quota
Peer-scoped.
339. Prevent one domain saturating ingress.
340. No user-level remote quota.
341. Hard rule.
342. Service-to-Service Quota
Internal services get bounded concurrency.
343. Avoid cascade.
344. Hard rule.
345. Autoscaling And Quotas
Scaling may increase total capacity.
346. Quotas still prevent burst dominance.
347. Hard rule.
348. Admission During Scale-Out
Do not assume new capacity instantly.
349. Continue load shedding/backpressure until healthy.
350. Hard rule.
351. Scale-In Draining
Before removing instance:
stop new work
drain
handoff
terminate
352. No kill active critical work.
353. Hard rule.
354. Spot/Preemptible Capacity
Optional for:
batch
background
analytics
355. Not critical control/security baseline.
356. Hard rule.
357. Capacity By Service Tier
Examples:
control-plane nodes
relay nodes
mailbox nodes
search nodes
media relays
358. Independent scaling.
359. No monolithic fleet scale.
360. Hard rule.
361. Relay Capacity
Scale by:
connections
bandwidth
CPU
queue
362. Not by identity.
363. Hard rule.
364. Mailbox Capacity
Scale by:
stored encrypted objects
delivery queue
I/O
365. No plaintext inspection.
366. Hard rule.
367. Search Capacity
Public search service only.
368. Private search local.
369. Good.
370. Media Relay Capacity
Scale by:
sessions
bandwidth
packet rate
371. No content inspection.
372. Hard rule.
373. Capacity Telemetry
Safe operational metrics:
queue depth
latency buckets
utilization
throughput
rejection rate
374. Forbidden:
stable user usage history
social graph
private content
375. Hard rule.
376. Capacity Telemetry Dimensions
Allowed:
service
region
work class
resource dimension
tenant aggregate if managed
377. No arbitrary user tags.
378. Hard rule.
379. Capacity Dashboard
Shows:
headroom
saturation
queue pressure
shed rate
autoscaling state
380. No user leaderboard.
381. Hard rule.
382. SLO Integration
Capacity should protect SLOs.
383. Examples:
message latency
security control latency
call setup latency
384. Under pressure
prioritize according to SLO/criticality.
385. Hard rule.
386. Availability Budget
Not same as error budget.
387. Capacity planning ensures headroom before SLO breach.
388. Good.
389. Admission Error Responses
Typed.
390. Example:
#![allow(unused)] fn main() { pub enum CapacityError { RetryAfter(DurationClass), QuotaExceeded, ServiceDegraded, CapacityUnavailable, } }
391. No revealing global fleet internals.
392. Hard rule.
393. Retry-After Privacy
Coarse duration.
394. Avoid unique timing fingerprint.
395. Hard rule.
396. Capacity Incident
Persistent critical saturation can open incident.
397. Not every peak.
398. Hard rule.
399. Capacity Abuse
If source exceeds fair share
rate-limit.
400. Does not imply malicious attribution.
401. Hard rule.
402. Compliance Integration
Part 95.
403. Controls:
bounded queues
protected security capacity
autoscaler min floor
headroom
regional reserve
404. No compliance through user tracking.
405. Hard rule.
406. Incident Integration
Part 96.
407. Capacity collapse can trigger incident.
408. Incident containment should not consume entire control pool.
409. Hard rule.
410. SOC Integration
Part 97.
411. Security floods/DoS can inform capacity response.
412. But SOC does not set user-specific resource priority.
413. Hard rule.
414. Vulnerability Integration
Part 98.
415. Emergency patch rollout may temporarily reserve update capacity.
416. Hard rule.
417. Update Integration
Part 99.
418. Security update traffic prioritized over routine downloads.
419. No blocking control plane.
420. Hard rule.
421. DR Integration
Part 100.
422. Maintain failover reserve.
423. During DR
shed optional work before critical restore/control traffic.
424. Hard rule.
425. Database Integration
Part 74.
426. DB pools bounded.
427. Background reconciliation cannot starve critical writes.
428. Hard rule.
429. Queue/Event Integration
Part 75.
430. Consumer lag drives backpressure/scale.
431. No unbounded replay storm.
432. Hard rule.
433. Consensus Integration
Part 76.
434. Quorum traffic protected.
435. No autoscaling that accidentally changes voter set.
436. Hard rule.
437. Discovery Integration
Part 77.
438. Newly scaled instances published only after health/readiness.
439. Hard rule.
440. Edge Integration
Part 78.
441. Edge admission/rate limiting.
442. Backend revalidates.
443. Hard rule.
444. East-West Integration
Part 79.
445. Per-service concurrency/rate budgets.
446. No trust in upstream admission alone.
447. Hard rule.
448. Secrets Integration
Part 80.
449. Autoscaled workload credentials issued dynamically.
450. No image-baked secret.
451. Hard rule.
452. Tenant Integration
Part 69.
453. Quotas/fairness scoped.
454. Personal anonymous usage independent.
455. Hard rule.
456. Federation Integration
Part 58.
457. Peer quotas and backpressure.
458. No transitive resource entitlement.
459. Hard rule.
460. Deployment Integration
Part 62.
461. Autoscaler only launches approved artifacts/config.
462. No dynamic arbitrary image.
463. Hard rule.
464. Host Integrity Integration
Part 71.
465. Scaled instances attested before sensitive traffic.
466. Hard rule.
467. Analytics Integration
Part 92.
468. Capacity metrics aggregate.
469. Product analytics never drives priority.
470. Hard rule.
471. Experimentation Integration
Part 93.
472. Capacity policy experiments only among safe equivalent policies.
473. No A/B weaker fairness/security.
474. Hard rule.
475. Audit Integration
Part 94.
476. Audit high-level changes:
quota policy changed
protected reserve changed
emergency brownout activated
477. Not every admission decision.
478. Hard rule.
479. Capacity Policy
Signed/versioned.
480. No dynamic arbitrary remote rule.
481. Hard rule.
482. Capacity Policy Example
#![allow(unused)] fn main() { pub struct CapacityPolicy { pub version: CapacityPolicyVersion, pub resource_budgets: Vec<ResourceBudget>, pub protected_capacity: Vec<ProtectedCapacity>, pub shedding: SheddingPolicy, pub autoscaling: AutoscalingPolicy, } }
483. Policy Anti-Rollback
Important if old policy lacks protections.
484. Hard rule.
485. Shedding Policy
#![allow(unused)] fn main() { pub struct SheddingPolicy { pub order: Vec<WorkClass>, pub brownout_thresholds: Vec<BrownoutThreshold>, } }
486. Critical classes cannot appear in ordinary shed list.
487. Type/runtime validation.
488. Hard rule.
489. Capacity Snapshot
#![allow(unused)] fn main() { pub struct CapacitySnapshot { pub state: CapacityState, pub resources: Vec<ResourceObservation>, pub queues: Vec<QueueObservation>, pub timestamp: CoarseTimestamp, } }
490. No user identity.
491. Hard rule.
492. Resource Observation
#![allow(unused)] fn main() { pub struct ResourceObservation { pub dimension: ResourceDimension, pub used: u64, pub available: u64, } }
493. Queue Observation
#![allow(unused)] fn main() { pub struct QueueObservation { pub class: WorkClass, pub depth: u64, pub age: Duration, } }
494. Privacy-safe.
495. Capacity State Evaluator
#![allow(unused)] fn main() { pub trait CapacityStateEvaluator { fn evaluate( &self, snapshot: &CapacitySnapshot, thresholds: &CapacityThresholds, ) -> CapacityState; } }
496. Load Shedding Controller
#![allow(unused)] fn main() { pub trait LoadSheddingController { fn actions( &self, state: CapacityState, policy: &SheddingPolicy, ) -> Vec<SheddingAction>; } }
497. Fair Scheduler
#![allow(unused)] fn main() { pub trait FairScheduler { fn schedule( &self, request: SchedulingRequest, ) -> SchedulingDecision; } }
498. Quota Service
#![allow(unused)] fn main() { pub trait QuotaService { fn consume( &self, scope: FairnessScope, resource: ResourceDimension, units: u64, ) -> Result<(), CapacityError>; } }
499. No billing side effect.
500. Hard rule.
501. Capacity Error Taxonomy
#![allow(unused)] fn main() { pub enum CapacityError { CapacityUnavailable, QueueFull, RetryLater, QuotaExceeded, BrownoutActive, AutoscalingLimitReached, ProtectedCapacityReserved, ScopeInvalid, Internal, } }
502. Capacity Observability
Safe metrics:
resource utilization
queue depth
shed rate
retry-later rate
scale events
headroom
503. Forbidden:
per-user lifetime consumption
behavioral priority profile
504. Hard rule.
505. Capacity SLOs
Examples:
critical-security admission latency
direct-message p95 latency
queue saturation duration
autoscaling reaction time
506. Privacy SLO
0 stable user IDs in autoscaling/admission telemetry
0 privacy-floor reduction under overload
507. Security SLO
0 critical-security starvation by optional work
0 unbounded queue in production
0 autoscaled untrusted artifact admitted
508. Failure Modes
traffic spike
dependency slowdown
autoscaler failure
database saturation
regional loss
509. Traffic Spike
Backpressure + scale + shed.
510. No uncontrolled queue growth.
511. Hard rule.
512. Dependency Slowdown
Circuit breaker/bulkhead.
513. Do not amplify retries.
514. Hard rule.
515. Autoscaler Failure
Static floor + brownout.
516. No scale-to-zero.
517. Hard rule.
518. Database Saturation
Protect critical pool.
519. Defer analytics/background.
520. Hard rule.
521. Regional Loss
Use DR reserve.
522. Shed noncritical to avoid secondary collapse.
523. Hard rule.
524. Capacity Testing
Need dedicated load/capacity testkit.
525. Test Scenarios
flash crowd
bulk upload storm
critical security event during saturation
regional failover load
autoscaler outage
526. Queue Bound Test
Queue cannot exceed item/byte limit.
527. Protected Capacity Test
Security task admitted during bulk saturation.
528. Fairness Test
One tenant cannot starve another.
529. Anonymous Fairness Test
No stable user identity required.
530. Brownout Test
Optional features shed first.
531. Privacy Test
No direct/anonymity downgrade under overload.
532. Retry Storm Test
Backoff/jitter prevents synchronization.
533. Circuit Breaker Test
Failing dependency isolated.
534. Autoscaling Hysteresis Test
No oscillating scale in/out.
535. Scale-In Drain Test
Active critical work not killed.
536. DB Saturation Test
Analytics cannot exhaust critical pool.
537. Mixnet Test
Cover traffic minimum preserved.
538. Realtime Test
Emergency call reserve preserved.
539. DR Test
Failover reserve survives normal peak.
540. Policy Rollback Test
Old weak capacity policy rejected.
541. Tenant Quota Test
A cannot consume B entitlement.
542. Federation Quota Test
One peer cannot flood all ingress.
543. Fuzzing
Fuzz:
capacity policy
admission request
quota token
brownout policy
autoscaling decision input
544. Property Tests
Properties:
critical-security work can never be shed by ordinary shedding policy
queue depth can never exceed configured hard bound
privacy floor can never be disabled by overload state
quota scope cannot authorize consumption outside its resource domain
545. Formal Verification Targets
Strong candidates:
capacity-state machine
protected-capacity invariant
fair scheduler starvation properties
autoscaling hysteresis
546. Kani Candidate
admission/shedding priority invariants.
547. TLA+ Candidate
load spike → backpressure → scale-out → brownout → recovery.
548. Loom Candidate
concurrent quota consume + queue admission + scale-state update.
549. Performance
Capacity control itself must be cheap.
550. Admission decision O(1) or near.
551. Metrics preaggregated.
552. Scheduler bounded.
553. No synchronous central coordinator for every request.
554. Hard rule.
555. Local Decisions
Prefer per-service/local node decisions within signed policy.
556. Global control only for:
fleet scaling
regional capacity
quota policy
557. Hard rule.
558. Cache Capacity State
Short TTL.
559. Stale state tolerated only conservatively.
560. No stale "capacity available" beyond hard limit.
561. Hard rule.
562. Storage
Separate:
capacity policy
quota config
autoscaling state
aggregate utilization
563. No per-user historical warehouse.
564. Hard rule.
565. Partitioning
By:
service
region
tenant aggregate
federation peer
work class
566. No user partition.
567. Hard rule.
568. Crate Layout
Recommended:
crates/
├── siar-capacity-core/
├── siar-resource-budget/
├── siar-admission-control/
├── siar-backpressure/
├── siar-fair-scheduler/
├── siar-quota/
├── siar-load-shedding/
├── siar-brownout/
├── siar-autoscaling/
├── siar-capacity-planning/
├── siar-capacity-observability/
└── siar-capacity-testkit/
569. siar-capacity-core
Owns:
CapacityState
WorkClass
ResourceDimension
errors
570. siar-resource-budget
Soft/hard limits/headroom/protected reserves.
571. siar-admission-control
Admission decisions/resource estimates.
572. siar-backpressure
Retry-after/retry budgets/circuit-breakers.
573. siar-fair-scheduler
Weighted fair queueing/priority/deadlines.
574. siar-quota
Tenant/anonymous/federation scoped quotas.
575. siar-load-shedding
Shedding order/policy.
576. siar-brownout
Feature degradation levels.
577. siar-autoscaling
Scale-out/in decisions/hysteresis.
578. siar-capacity-planning
Forecast/headroom/failure-reserve modeling.
579. siar-capacity-observability
Aggregate operational pressure metrics only.
580. siar-capacity-testkit
load/fairness/privacy/autoscaling tests.
581. Security, Privacy & Correctness Invariants
Mandatory:
1. Every production queue, pool, concurrency limiter, and retry path has explicit hard bounds; no unbounded backlog is allowed to become the overload strategy.
2. Work priority is based on semantic system criticality—security, emergency, control, messaging, interactive, background, bulk—not user identity, wealth, engagement, or behavioral profile.
3. Protected capacity for critical security, emergency, and control-plane work cannot be consumed by optional, bulk, analytics, or background workloads.
4. Overload responses may defer, degrade, backpressure, shed, or reject work, but can never disable encryption, anonymity, authorization, tenant isolation, or other privacy/security floors.
5. Anonymous-user fairness uses scoped capabilities, short-lived quotas, connection/resource tokens, or other unlinkable mechanisms rather than stable global identities.
6. Tenant and federation-peer fairness is scope-isolated; one tenant or peer cannot monopolize shared resource pools or gain access to another scope's quota state.
7. Autoscaling uses aggregate operational resource signals such as CPU, memory, queue depth, throughput, latency, and connection count—not private content or user behavioral histories.
8. Brownout and load-shedding policies remove optional/background/bulk work before direct messaging, emergency, security, and control-plane functionality.
9. Retry, circuit-breaker, bulkhead, and backpressure policies prevent cascading overload and synchronized retry storms.
10. Scale-in, failover, and maintenance operations drain or hand off critical work safely and never assume capacity exists before new instances are healthy, trusted, and admitted.
11. Capacity observability contains aggregate service/region/work-class pressure only and cannot become a per-user usage, social, or behavioral analytics system.
12. Capacity management integrates with quotas, rate limiting, DR, autoscaling, deployment, tenant isolation, federation, security operations, and updates without creating an alternate authorization or privacy-downgrade path.
582. Initial Production Scope
Implement first:
typed ResourceDimension/WorkClass/CapacityState
hard/soft resource budgets
bounded Tokio channels
concurrency semaphores
protected capacity for security/control traffic
admission controller
retry budgets/backoff/jitter
circuit breakers
bulkhead isolation
weighted fair scheduling
tenant/federation quotas
anonymous scoped resource tokens
load-shedding order
brownout levels
autoscaling with hysteresis/cooldown
regional headroom/failover reserve
DB connection-pool isolation
mixnet cover-traffic floor
realtime emergency reserve
privacy-safe capacity metrics
capacity testkit
Then add:
advanced forecasting
multi-region global capacity optimizer
anonymous blind quota tokens
cost-aware heterogeneous scaling
formal scheduler/fairness verification
dynamic capacity reservation marketplace where compatible with privacy/economic architecture
583. Definition of Done
Part 101 is complete when:
- all queues and resource pools are bounded
- semantic priority classes are explicit
- critical/security/control traffic has protected capacity
- admission/backpressure/shedding state machines exist
- retries cannot amplify overload indefinitely
- anonymous fairness works without stable identity
- tenants/federation peers cannot starve each other
- brownout disables optional work before core features
- autoscaling uses aggregate privacy-safe signals
- scale-in drains safely
- regional reserve supports failover
- overload never weakens privacy/anonymity/security
- capacity telemetry contains no behavioral user profiles
- load/fairness/autoscaling/privacy/fuzz/formal tests are specified
584. Final Architecture
INCOMING WORK
│
▼
ADMISSION CONTROL
│
▼
PRIORITY + FAIRNESS CLASS
│
┌────────────┼────────────┐
│ │ │
PROTECTED NORMAL OPTIONAL
CAPACITY POOLS POOLS
│ │ │
└────────────┼────────────┘
▼
BOUNDED EXECUTION
│
┌───────┼───────┐
│ │ │
EXECUTE DEFER SHED
│
▼
CAPACITY FEEDBACK
│
AUTOSCALE / BROWNOUT
Capacity safety model:
hard resource bounds
+
protected critical capacity
+
fair admission
+
backpressure
+
load shedding
+
brownout
+
privacy-safe autoscaling
+
failure reserve
not:
accept everything, queue forever, let low-value work consume every resource, then drop privacy guarantees when the system collapses
585. Final Principle
Availability is not achieved by serving every request at any cost; it is achieved by preserving the right work under pressure.
The correct model is:
bound everything
+
reserve critical capacity
+
admit fairly
+
backpressure early
+
shed low-value work first
+
scale from aggregate signals
+
preserve privacy floors
+
recover gradually
This architecture gives SIAR a privacy-preserving availability foundation for admission control, resource fairness, load shedding, autoscaling, brownout, multi-tenant isolation, anonymous quotas, regional reserve, realtime capacity, mixnet capacity, and overload recovery while preserving the anonymity, local-first, least-authority, and anti-surveillance guarantees established across Parts 34–100.